Alsebra has the right idea here. You can run this as a one-of to REPEAT the effect multiple times on a turn, churning away your library until you've got a library full of flashback cards/zombies, or you can make sure you have one or two Laboratory Maniacs in your hand (along with a counterspell or two, of course) as a risky win condition.

I think the flavor works better if you run this in multiples. A crazed phantasm skittering through a mansion full of mirrors, making you lose your mind, and your spells as a consequence. Really good. 3.5 for combo potential, bumped up to 4 for flavor.

@Faralay: If you're looking for the Laboratory Maniac alt win condition, only run one Mirror-Mad Phantasm, copy it with something like Evil Twin or Cackling Counterpart, then activate it. Because it explicitly states that you're looking for a card named Mirror-Mad Phantasm, you'll never find it if it's been copied or is being represented by a token (as per the FAQ).

And yes, protect the Lab Maniac with everything you got. Mask of Avacyn, counters, whatever.